"What we should do is focus on ISIS. We should not be focusing on Syria," Trump said in an interview with Reuters. "You're going to end up in World War Three over Syria if we listen to Hillary Clinton."

The Syrian conflict is a complex web of competing local and international influence that began in 2011 as peaceful protests against President Bashar al-Assad, but for the past two years has also included a fight against Islamic State militants. Russia and Iran back Assad against the rebels, while opposition fighters have support from countries such as the United States, Turkey and Saudi Arabia.

Assad's role

Clinton has proposed in many ways continuing U.S. efforts to go after Islamic State fighters and wants Assad to leave power. But she also supports establishing a no-fly zone in order to protect civilians, something President Barack Obama has resisted and which would potentially set up conflict with Syrian and Russian forces.

Trump told Reuters Assad's role in the future of Syria is "secondary" to the goal of defeating Islamic State, and that the Syrian leader is stronger today than he was three years ago.

"Once again, he is parroting Putin's talking points and playing to Americans' fears, all while refusing to lay out any plans of his own for defeating ISIS or alleviating humanitarian suffering in Syria," said a statement from Clinton spokesman Jesse Lehrich.

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Trump also repeated his assertion that the media is rigging polls to show he is behind Clinton, and criticized the Republican Party for what he called a lack of support.

"The people are very angry with the leadership of this party, because this is an election that we will win 100 percent if we had support from the top. I think we're going to win it anyway," he said.

Trump's campaign finance chairman, Steven Mnuchin, made the unusual announcement that Trump will no longer take part in big-money fundraisers that are key for the Republican Party to support congressional candidates.

Trump Victory, a joint fundraising committee by the party and the presidential candidate's campaign, is now "wound down" after holding its last event last week, Mnuchin told The Washington Post. The candidate himself will spend the last two weeks of the campaign holding rallies and taking his message directly to the voters in person, he added.